For every few steps forward Manchester United take this season, a jolt to the senses seems obligatory. This was a significant blow to their hopes of fourth place, leaving them sixth in the Premier League, and the frustration was that the performance was not especially bad.

In fact, Mata's irresponsible first half red card, picking up two needless bookings in as many minutes, made it hard to put a measure on what followed. The bare truth is that Salomon Rondon's 66th minute winner, swept home expertly after Sebastien Pocognoli's cross found him unmarked in the area, gave West Brom a win they eventually deserved and tempered the enthusiasm sparked by United's recent upturn.

Despite Mata's 26th minute dismissal, the first half progressed broadly to type. Craig Dawson, the home right-back, miscued an early header from Rondon's cross and Chris Smalling was sharp to block from the lively Saido Berahino. It was Craig Dawson, looping a 30-yard half-volley over David De Gea but inches wide of the far post while Mata was still walking to the showers, who came closest to breaking the deadlock. But there was little indication that either side had the craft to penetrate the massed ranks in front of them.

Perhaps encouraged to make more urgent use of a quicksilver front three after Mata had departed, United began the second half at speed. Marcus Rashford, for whom this fixture provided a fascinating litmus test, had been quiet before the break but saw a snap shot deflected just off target six minutes after half-time. Jesse Lingard, who had by now swapped to the left flank, whipped an angled effort over shortly afterwards. There was a heart-in-mouth moment for Jonas Olsson, who was booked for fouling a rampaging Anthony Martial but the Ander Herrera's free-kick came to nothing.

Yet West Brom rode the mini-storm. Pocognoli, who had replaced the injured Dawson and come on at left-back -- James Chester moving to the right -- had already laid on a half-chance for Berahino when his accurate low delivery teed up Rondon's winner.

The Venezuelan should not have been given time to control and shoot to De Gea's left, but something generally has to give when you are down to 10 men. United, who huffed and puffed after that but never looked like equalising, were left to rue Mata's act of indiscipline.

Salomon Rondon's goal gave West Brom their first home league win over Manchester United in the Premier League.

2. Mata dismissal wrecks visitors' hopes

The foul was all the more mystifying for coming from a player who normally operates with such a clear head. Mata had been central to United's recent improvement and probably in the best form of his time at the club -- an inventive, constantly available presence providing timely prompts for a young, raw attack. Four days before this game he had scored a fine late free kick to defeat Watford and a 24th minute yellow card for encroaching at a West Brom free kick seemed of little consequence to a fairly encouraging start at the Hawthorns.

That was until only two minutes later, when Darren Fletcher shifted up the gears for West Brom. The former United midfielder had shown a useful burst of pace to outstrip Mata but was midway inside his own half and any danger was distant. Mata's challenge -- more a petulant slash at Fletcher's ankle than anything resembling a tackle -- was as unnecessary as they come and gave Mike Dean one of the easier red card decisions he will be faced with this season. It was the first dismissal of Mata's career and United's first this season. It was a moment entirely out of keeping from a player, and team, who do not exactly operate as if on the edge.

Mata's teammates persevered. Smalling, sniffing danger that split-second ahead of anyone time and again, was outstanding at the back and their front players worked tirelessly to reverse the tide. That the goal arrived during West Brom's first genuine spell of sustained pressure after the break was cause for annoyance, but the biggest regret was that this had seemed like a genuine opportunity for United to cement their best league run since September. Had Mata mustered anything like the composure he usually emits, his team's season might be looking very different now.

Juan Mata's dismissal in the first half left Manchester United with a mountain to climb.

3. Tony Pulis does it again as Baggies sense safety

Pulis knows the "style versus substance" debate as well as anyone. This victory put West Brom on 39 points and means that relegation is unthinkable with nine games to go. It is highly plausible they will at least match the club's record haul in the Premier League era, 49, and that is no small achievement from a side that generally goes unnoticed when there is little to say about the much-debated future of Berahino.

The striker's work rate has pleased Pulis of late and he certainly fitted into the schema here, notionally playing up alongside the tireless Rondon but regularly tracking back to help his teammates and also coming close to a goal when jabbing Pocognoli's cross just off target.

With West Brom's security assured, what use Pulis chooses to make of Berahino -- constantly linked away from the club -- remains to be seen. West Brom play to such a tight formula, regrouping smartly as soon as the ball is lost and springing forward via the flanks when it is recovered, that they will pose anyone a challenge without him.

That is to Pulis' immense credit. West Brom do not have the craft and guile of many around them but their manager's ability to dig his teams into a foothold in this league is only to be admired. Regardless of what they achieve, and how they achieve it, in the next two months, Pulis' primary task is complete.

Nick Ames is a football journalist who writes for ESPN FC on a range of topics. Twitter: @NickAmes82.